Micromechanical or semiconductor fabrication techniques are known for producing micromechanical transducers such as accelerometers, gyroscopes, pressure sensors and the like. Generally, a micromechanical transducer element, fabricated by doping and selectively etching semiconductor materials, is displaced by a parameter (e.g., inertia, pressure) the magnitude of which is to be determined. The amount of displacement may be made linearly proportional and output as an indication of the magnitude of the desired parameter. Typically, such transducers are "rebalanced" or driven back to a null or rest position by applying a voltage to the transducer element. This kind of "electrostatic" rebalance is exemplified in U.S. Pat. No. 4,483,194 to Rudolf, which discloses electrodes parallel to the plane of a semiconductor carrier, which apply the electrostatic rebalance torque to the transducer element.
However, electrostatic rebalance using only electrodes below the transducer element may result in an uneven net force between the transducer and the electrodes, causing asymmetric attractive forces therebetween, resulting in undesirable scale factor variation with input and torque bias.
Electrodes may be implemented above and below the transducer element with top to bottom symmetry to preclude uneven net force. However, fabricating symmetrical electrodes above the transducer element adds significant, additional processing steps and resultant cost.